Ultrasonic biometric imaging and identity verification system

ABSTRACT

An ultrasonic imaging system and method for imaging human or animal tissue having a surface and including a probe comprising a platen for defining the surface in a manner supporting the human or animal tissue for imaging the same, a transducer positioned closely adjacent the supporting platen for providing an output ultrasonic beam directed on the surface so that the size of the beam at its focal point is as small as possible to maximize the resolution of the system an electrically operated motor for moving the transducer in a manner such that the ultrasonic beam is directed in a path along the surface. A fluid-tight housing extends from the tissue-supporting surface and has an interior region containing the transducer and motor which region is filled by an electrically non-conductive fluid having an acoustic impedance substantially equal to that of water and having a viscosity sufficiently low so as not to impede the movement of the transducer. The housing is provided with a bellows for accommodating thermal expansion and contraction of the fluid. In one aspect of the invention, the motor provides oscillatory output motion and the output shaft is coupled to the transducer so that in response to oscillation of the shaft the output ultrasonic beam is directed in the path along the surface. An encoder is mounted on the shaft between the motor and coupling to minimize any distortion in the information provided by the encoder. The coupling is in the form of an elongated arm having a structure of sufficient rigidity so as not to bend or flex during oscillation of the motor shaft while having minimal drag as the arm moves through the fluid.

This is a continuation of Ser. No. 08/892,634 filed Jul. 15, 1997 andnow U.S. Pat. No. 5,935,071, and is a division of Ser. No. 08/389,104filed Feb. 15, 1996 and now U.S. Pat. No. 5,647,364.

BACKGROUND OF THE INVENTION

This invention relates to the art of surface scanning and imaging, andmore particularly to a new and improved ultrasonic method and apparatusfor surface scanning and imaging.

One area of use of the present invention is in fingerprint scanning andimaging, although the principles of the present invention can bevariously applied to scanning and imaging subdermal and other biometricstructures. The quality of the images obtained using ultrasoundtechnology is superior as compared to those obtained using opticaltechnology since the ultrasonic images are less dependent on the surfacecondition of the finger. As a result, by using ultrasound technology,individuals with very dry or very oily fingers, contaminated fingers orfingers having irregular ridge surfaces are able to be imaged equally aswell.

In providing an ultrasonic method and apparatus for scanning and imagingfingerprints, subdermal and other biometric structures, there are anumber of important considerations. One is obtaining higher qualityimages which, in turn, requires that the resolution of the system be ashigh as possible so that the resolution of the resulting images is ashigh as possible. Another important consideration is improved systemperformance. One example is performing the scanning as quickly aspossible so as to minimize delay and inconvenience and avoid anydiscomfort to the individual. Related to the foregoing considerations isincreased reliability of the system and its operation. Additionalimportant considerations are ease of manufacture and lowering the costof manufacture.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of this invention to provide a newand improved ultrasonic method and apparatus for imaging human andanimal tissue.

It is a more particular object of this invention to provide such amethod and apparatus which results in high resolution and high qualityimages.

It is a further object of this invention to provide such a method andapparatus wherein scanning is performed at a very fast rate.

It is a further object of this invention to provide such a method andapparatus which is highly reliable.

It is a further object of this invention to provide such apparatus whichis relatively easy and economical to manufacture.

The present invention provides an ultrasonic imaging system and methodfor imaging human or animal tissue having a surface and including probemeans comprising means for defining the surface in a manner supportingthe human or animal tissue for imaging the same, transducer meanspositioned closely adjacent the supporting means for providing an outputultrasonic beam directed on the surface so that the size of the beam atits focal point is as small as possible to maximize the resolution ofthe system and electrically operated motive means for moving thetransducer means in a manner such that the ultrasonic beam is directedin a path along the surface. A fluid-tight housing means extends fromthe means defining the tissue-supporting surface and has an interiorregion containing the transducer means and motive means which region isfilled by an electrically non-conductive fluid having an acousticimpedance substantially equal to that of water and having a viscositysufficiently low so as not to impede the movement of the transducermeans. The housing is provided with means for accommodating thermalexpansion and contraction of the fluid. In one aspect of the invention,the motive means comprises motor means having an output shaft forproviding oscillatory output motion and means for coupling the outputshaft to the transducer means so that in response to oscillation of theshaft the output ultrasonic beam is directed in the path along thesurface. An encoder means is mounted on the shaft between the motor andcoupling means to minimize any distortion in the information provided bythe encoder means. The coupling means is in the form of an elongated armhaving a structure of sufficient rigidity so as not to bend or flexduring oscillation of the motor shaft while having minimal drag as thearm moves through the fluid.

The transducer is oscillated about successive arcuate paths along thearea being scanned, and a two dimensional linerization process isperformed on the data obtained.

In alternative embodiments, the oscillatory output of the motor can beassisted by a flexure spring means, the transducer can be moved by acontinuously rotating motor with a slip-ring commutator for makingelectrical connection to the transducer, and the transducer can be movedlinearly in orthogonal directions by the combination of a rotary motorwith motion conversion means and a linear actuator.

The scanner of the present invention can be employed in biometricidentification and verification systems wherein the imaging system isutilized in combination with a record member containing a recordedbiometric image and a processor for performing comparisons.

The foregoing and additional advantages and characterizing features ofthe present invention will become clearly apparent upon a reading of theensuing detailed description together with the included drawing wherein.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a longitudinal sectional view, partly in elevation, of anultrasonic probe according to the present invention for surface scanningand imaging;

FIG. 2 is a top plan view with parts removed of the probe of FIG. 1;

FIG. 3 is a bottom plan view with parts removed of the probe of FIG. 1;

FIG. 4 is a longitudinal sectional view of the expansion bellows in theprobe of FIG. 1;

FIG. 5 is an end elevational view, taken from the right as viewed inFIG. 4, of the expansion bellows;

FIG. 6 is a side elevational view of the coupling arm of the probe ofFIG. 1;

FIG. 7 is a top plan view of the arm of FIG. 6;

FIG. 8 is an enclosed fragmentary elevational view of the coupling armof the probe of FIG. 1 in relation to an arm position sensor;

FIG. 9 is a diagrammatic view of an alternative form of platen for usein the probe of FIG. 1;

FIG. 10 is a block diagram of a bilinearization processor for use inconjunction with the probe of FIG. 1;

FIGS. 11A, 11B, 11C and 11D comprise a block diagram of a systemcontaining the probe of FIG. 1;

FIGS. 12, 13, 14A, 14B and 15-16 are diagrammatic views of alternativearchitectures for moving the transducer during scanning in a probe ofthe type shown in FIG. 1;

FIG. 17 is a block diagram illustrating the use of the scanner of thepresent invention in an identification system;

FIG. 18 is a block diagram of a wireless version of the system of FIG.17;

FIGS. 19 and 20 are block diagrams illustrating the use of the scannerof the present invention in a verification system; and

FIG. 21 is a block diagram illustrating a wireless version of the systemof FIG. 20.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In a basic ultrasonic scanning and imaging system a probe assembly isthe part of the system that is responsible for the motion of atransducer in order to obtain a two dimensional scan window, typicallyhaving dimensions of 0.75″×0.75″ for fingerprint imaging. The motion ofprobe assembly is controlled by electronics of a scan controller whichcontains the necessary motor driver logic needed to drive the motors ofthe probe assembly. The data out of the transducer of the probe assemblyis then received by a signal processor where amplification, rangegating, peak detection and A/D conversion take place. This data isstored in a high speed data buffer random access memory which isinterfaced to any device suitable for receiving and processing the rawfingerprint data. A device such as a general purpose computer or customfingerprint image processor could be used for this purpose. All of thesystem components or subassemblies are powered by a power supply whichprovides the necessary voltages for operating the system.

One of the applications for the technology of the foregoing system isobtaining dermatoglyphics or images of the friction skin surface of thefinger, namely the fingerprint. The quality of the images obtained usingultrasound technology over optical technology is superior since theseimages are less dependant on the surface condition of the finger. Thisis discussed in detail in U.S. Pat. No. 5,224,174 issued Jun. 29, 1993and entitled Surface Feature Mapping Using High Resolution C-ScanUltrasonography, the disclosure of which is hereby incorporated byreference. As a result, individuals with very dry or very oily fingers,contaminated fingers or fingers having irregular ridge surfaces are ableto be imaged equally as well. Furthermore, other human and animal tissuesurfaces can be scanned, such as palms, toes and the like.

A second fundamental advantage in the use of the ultrasound forfingerprint imaging is using subdermal features that are found withinthe finger to reproduce the friction skin image. This is useful when theridge detail on the outer surface of the finger has been temporarilymodified such as-by small cuts, destroyed altogether, or is notdiscernible due to excessive wear. The immediate underside of the skincontains all of the detail that the surface friction skin does;therefore, by imaging the immediate underside of the epidermis, afingerprint image can be obtained free from any defects that might bepresent on the outer surface of the finger. The second or dermal layerof skin also contains artifacts that correspond to the dermatoglyphicsof the friction skin. This layer of skin is composed of structures knownas dermal papillae which are arranged in double rows where each row liesin a ridge of the epidermal layer. The only modification in the systempreviously described that is required to obtain the subdermal imagesjust below the epidermis is to process the ultrasonic signals returnedfrom this depth and not the surface. This is accomplished by adjusting arange gate. The range gate is a window used to allow a particularportion of the return signal to propagate to the signal processingelectronics; therefore, delaying the range gate in time corresponds toimaging deeper into the finger.

This technique of subdermal imaging could prove particularly useful forthose individuals whose friction skin lacks sufficient detail foranalysis. This includes individuals who have undergone some form oftrauma to the finger or hand, ranging from the very minor such as smallcuts on the surface of the finger to the more severe such as burnvictims. This technique would also prove beneficial in imaging otherswhose occupation tends to wear the ridge structure off from the surfaceof the finger. Since together these groups of individuals represent asignificant percentage of the population, other devices that cannotimage below the surface of the finger, such as the optical fingerprintreaders, are at a clear performance disadvantage.

A third potential for the application of the technology of the foregoingsystem lies in the development of an entirely new biometric. It is wellknown that blood vessel patterns throughout the body have been used as ameans of personal identification. Generally, the techniques that must beemployed to obtain these images are deemed intrusive by the user andtherefore such techniques generally do not succeed in a commercial massmarket environment. The system described herein has the capability topenetrate well beneath the surface of the finger and image blood vesselsand other subdermal structures. These structures are highly numerous andcontain sufficient information to positively identify an individual. Anentirely new biometric could be developed with the expectation that thisbiometric could prove to be much simpler in the post processingnecessary to identify an individual using the fingerprint. Thesimplicity results in higher processing throughputs, greater accuracy,and lower system complexity, which in turn results in reduced systemcost.

As previously described, in an ultrasonic scanning and imaging systemthe probe is the part of the system that is responsible for the motionof the transducer in order to obtain a two dimensional scan window fortissue imaging. In a basic probe arrangement, there is provided a platenfor defining a surface in a manner supporting human or animal tissue forimaging the same, a transducer for providing an output ultrasonic beamand positioned closely adjacent the platen, first motive means formoving the transducer to direct the ultrasonic beam along the surface ina first direction and second motive means for moving the transducer todirect the beam along the surface in a second direction. In order tominimize attenuation of the ultrasonic energy as it propagates to thetissue being imaged, the transducer is positioned in a liquid-filledregion, i.e. in a water filled cavity. This required, in the foregoingarrangement, establishing a water tight seal in two places on the probe.One seal is a flexible or oscillating seal between the first motivemeans and the transducer. The second seal is a large bellows responsiblefor forming the overall liquid cavity. The foregoing basic probearrangement is shown and described in pending U.S. patent applicationSer. No. 08/147,027 filed Nov. 4, 1993 entitled “High ResolutionUltrasonic Imaging Apparatus and Method” and assigned to the assignee ofthe present invention, the disclosure of which is hereby incorporated byreference.

Thus the basic concept of the foregoing arrangement was that byemploying a flexible rubber bellows and oscillating seal, a fluid tightcavity was created. The cavity was filled with water, and the water wascontained by the seals, preventing it from contacting the electricallyoperated motive means which otherwise would cause a short circuit. It isan objective of the present invention to eliminate the two seals, i.e.,flexible bellows and oscillating seal, so as to increase the reliabilityof the probe and simplify its structure and manufacture. This isaccomplished according to the present invention by submersing both themotive means or motors in the fluid which, in turn, must be anelectrically non-conductive fluid having a low viscosity and acousticimpedance near that of water.

Referring now to FIGS. 1-3 a probe generally designated 10 according tothe present invention comprises means in the form of a platen 12 fordefining a surface 14 in a manner rigidly supporting human or animaltissue for imaging the same and transducer means 16 for providing anoutput ultrasonic beam and positioned closely adjacent supporting means12 in a manner directing, i.e. focusing, the ultrasonic beam on thesurface 14 and so that the size of the beam at its focal point is assmall as possible to maximize the resolution of the system. There isprovided electrically-operated motive means generally designated 20operatively coupled to transducer means 16 for moving transducer means16 in a manner such that the output ultrasonic beam is directed in apath along surface 14. The motive means 20 will be described in detailpresently.

In accordance with the present invention, there is provided fluid-tighthousing means generally designated 26 extending from platen 12 andhaving an interior region 28 containing transducer means 16 andmotive-means 20. Also in accordance with the present invention theinterior region 28 of housing means 26 is filled with fluid 30. Thus, ascan be seen, each of the subassemblies 16 and 20 now reside internal tothe sealed cavity 28. This eliminates the need for the oscillating sealand bellows. Eliminating both of these devices removes potential pointsof failure, increasing system reliability. Furthermore, eliminatingthese two components simplifies the overall complexity of the mechanicalframe and reduces assembly time which results in a cost reduction inmanufacture of probe 12.

In order for the subassemblies 16 and 20 to operate submersed in thefluid, a fluid must be selected which is electrically non-conductive. Inaddition to its non-conductivity, the fluid must also have an acousticimpedance to nearly match that of water so as not to attenuate the highfrequency ultrasound. The fluid should have an acoustic phase velocitynear that of water so as not to alter the focal length of transducer 16.Another property that the fluid of interest must have is low viscosityso as not to impede the motion of the transducer. It is also importantfor the fluid to have low air solubility. There are several fluids thatmeet these requirements and are well known to individuals skilled in thefield of ultrasonic imaging. By way of example, in an illustrativeprobe, fluid 30 is a white petroleum-based mineral oil commerciallyavailable from Witco Chemical Corporation under the designation Klearol.

Housing means 26 includes cover assembly 36 which contains platen 12,first and second sidewalls 38 and 40, respectively, extending from cover36 and joined by a bottom wall 40 and first and second end walls 42 and44, respectively. The side and end walls are joined to cover assembly 36by suitable means such as fasteners 48 and a continuous seal or gasket50 is fitted in a peripheral recess in the joint between the walls andcover to provide a fluid-tight connection. Similarly, bottom wall 40 isjoined to the side and end walls by suitable means such as fasteners 54and a continuous seal or gasket 56 is fitted in a peripheral recess inthe joint between bottom wall 40 and the side and end walls to provide afluid-tight connection. In the probe assembly shown, one of the endwalls, in particular end wall 44, carries an extension which isgenerally hollow rectangular in shape defined by top and bottom walls 60and 62, respectively, a pair of side walls 64 and 66 and an end coverassembly 68. The extension houses a component of motive means 20 andother probe components which will be described. The interior of theextension is in fluid communication with cavity 28 via openings orpassages in end wall 44.

Depending upon the environment to which probe 10 is exposed duringtransport, storage and use, various ambient temperature conditions willbe encountered. Temperature variations of a significant magnitude cancause expansion and contraction of fluid 30. In other words, once thecavity 28 has been filled and purged of all air, it is sealed. As theoil 30 experiences thermal fluctuations due to its surroundingenvironment, it undergoes thermal expansion and contraction. Inaccordance with the present invention, housing 26 is provided with meansfor accommodating thermal expansion and contraction of fluid 30. In theprobe apparatus shown, a flexible expansion bellows generally designated76 is provided in the extension from end wall 44. As shown in FIGS. 4and 5, bellows 76 comprises a small rubber diaphragm element having acylindrical wall portion 78 which is closed at one end by a wall 80 andopen at the other end which terminates in a peripheral flange 82. Asshown in FIG. 2, bellows 76 is mounted in an opening in extension topwall 60 by a mounting plate 84 having a central opening 86 and securedby fasteners 88. The diaphragm or bellows 76 is totally free to move inand out as required. The size of diaphragm 76 is selected to have enoughflexibility to accommodate the total thermal expansion experienced forthe specified temperature range of probe 10. Diaphragm 76 is made of aneoprene rubber impervious to degradation by the hydrocarbon based oil30.

Motive means 20 includes first means 90 for moving transducer 16 todirect the ultrasonic beam along the surface 14 in a first direction andsecond means 92 for moving transducer means 16 to direct the beam alongthe surface in a second direction. The first direction is into and outof the plane of the paper as viewed in FIG. 1 and the second directionis in the plane of the paper from left to right as viewed in FIG. 1. Inthe probe assembly shown, the first means 90 comprises motor means foroscillating transducer 16 to move the ultrasonic beam in an arcuate pathalong surface 14, and the second means 92 comprises motor means formoving transducer 16 to move the ultrasonic beam in a linear path alongsurface 14. Thus the probe 10 performs a two dimensional scan geometryof the human or animal tissue supported on surface 14.

The transducer 16 is mounted to a probe arm 100 by suitable means suchas adhesive, which arm 100 is attached to the shaft of the motor 90creating an arc to be swept out each time the motor moves through itspredefined angle of rotation. The transducer is positioned directlyunder the platen 12 in which the finger to be imaged is placed. Arm 100will be described in detail presently.

Once a single line has been scanned, the second motor means 92 in theform of a linear actuator motor is used to move the entire assemblyalong the second axis of motion, where a second line is scanned. Thisprocess is repeated until an equivalent scan area, for example an areaof 0.75″×0.75″, has been imaged. Upon completing the scan, linearactuator 92 is rewound to its starting position as indicated by aposition sensor which will be described in further detail presently.

The probe 10 of the present invention includes position feedback meansgenerally designated 110 operatively associated with motor means 90 inorder to provide feedback information to the system control as to therotational position of motor 90. In the probe shown the positionfeedback means comprises encoder means. In accordance with the presentinvention the encoder is mounted on the output shaft 112 of motor 90between motor 90 and arm 100. Thus, the optical encoder is mounteddirectly under the probe arm and is immersed entirely in the fluid 30.In this connection, fluid 30 must be optically clear so as not tointerfere with performance of encoder 110. The placement of the opticalencoder is critical to the overall image quality. In a previousarrangement, the optical encoder was mounted on the shaft of one side ofthe oscillatory motor and the probe arm was mounted on the other side ofthe oscillatory motor at the opposite end of the shaft. Thus, anytwisting of the shaft over the span was seen directly by the opticalencoder. This twisting caused the probe arm to be pointing in onedirection while the optical encoder read a different direction. In theprobe 10 of the present invention, the encoder 110 is mounted directlyunder the probe arm 100. This reduces the total shaft length seenbetween the probe arm and the encoder. As such, the total amount ofshaft flex between the two components is minimized. This, in turn,minimizes the amount of registration distortion in the image.

A second improvement to the optical encoder can be found in the mountingtechnique. Previously, the encoder was mounted using a single set screwtightened onto the motor shaft. This set screw was not strong enough tosecurely attach the optical encoder to the motor shaft, again resultingin movement of the optical encoder with respect to the probe arm. Thenew mounting technique employed in probe 10 uses a press fit joint tosecurely attach the encoder 110 to the shaft 112 of the motor 90. Theshaft is knurled prior to mounting the encoder and the encoder is pressfit over the knurl. The result is a joint of high integrity severaltimes stronger than the set screw approach.

A third improvement to the optical encoder is increased resolution.Previously, the encoder was 512 lines per revolution. However, due tothe increased probe arm length, which will be described, in order tomaintain the required resolution for scanning the finger, the resolutionof the optical encoder must be increased to 1024 lines per revolution.The angular pixel resolution together with the length of the probe armresults in a scan sample every 0.002″.

A fourth improvement in the optical encoder is in the addition of athird channel for absolute position indication. Prior to every scan, theoptical encoder electronics needs to be reset. This results in a zeroreference indicator to be the current position of the probe arm 100 andoptical encoder subassembly. From this position the system softwarecauses the probe arm to scan an angle symmetric around the zeroreference. Thus, if the motor 90 does not return to the same positionafter every scan, the arc which is swept out varies from scan to scan.This results in different areas of the finger to be scanned along withimage distortion caused by the bilinearization software which will bedescribed. Adding a third channel to the optical encoder gives anabsolute position indication. This absolute position timing mark can bereferenced to the zero reference of the optical encoder. Each scan canthen be adjusted automatically in software to keep the differencebetween these two numbers a constant. This results in very repeatableimages without any distortion from the bilinearization software.

A fifth improvement relates to the encoder sensor. In a previousconfiguration, the optical code wheel and the encoder sensor electronicswere purchased as a single integrated unit. Deficiencies were found inthis arrangement. Specifically, the mounting of the sensor with respectto the code wheel was implemented using plastic. The plastic did notprovide a rigid enough mount for the stresses placed on it due to theoscillatory motion of the motor. As such, the electronics wouldphysically move with respect to the code wheel causing extra outputpulses. These output pulses were interpreted as Main Bangs and as such,caused extra data points to be captured. This had the net effect ofcontributing to the line to line misregistration of the image. As aresult, the encoder sensor and optical encode wheel are no longer usedas an integrated assembly but instead are mounted separately. Thisensures that the mounting of the encoder sensor can be done in such afashion so that it is rigid enough to prevent any movement with respectto the encode wheel. This is accomplished by mounting the sensor 118onto the aluminum motor base plate 120 in which the motor 90 is mounted.The base plate 120 is much more rigid than the previous plastic mountsand prevents any movement of the sensor 118. The encoder wheel isdesignated 119 in FIGS. 1 and 2.

By way of example, in an illustrative probe, encoder 110 is commerciallyavailable from Hewlett Packard under the designation HEDS-6140 for thecodewheel and HEDS-9040 for the encoder sensor 118. The ability of thatparticular sensor to operate submersed in oil 30 can be enhanced byplacing a clear transparent cover over the guarding to encapsulate theLED and lens and prevent oil from coming in contact with the lens.

While the optical encoder was chosen due to its simplicity, ease of useand low cost, other positional feedback devices can be employed. Twowhich appear to show promise are the capacitive encode wheel and therotary potentiometer. The capacitive code wheel is simply two plates(electrodes) separated by a small distance. The electrodes are shapedsuch that the amount of area each electrode overlays the other varies asa function of its rotational position. As such, the overall capacitancevaries with respect to rotational position. As in the case of theoptical encoder, both absolute and relative encoders are availabledepending on the electrode deposition pattern. As in the case of theoptical encoder, capacitive encoders will also work submersed in oil.The rotary potentiometer is a small, low inertia device that mounts tothe motor shaft and provides a resistance output as a function ofangular position. The rotary potentiometer has many of the attributes ofoptical encoders and capacitive encode wheels.

As previously described, transducer 16 is mounted to one end of probearm 100, the other end of which is attached to shaft 112 of motor 90.The elongated probe arm 100, which is responsible for holding theultrasonic transducer 16, must be rigid enough to not flex or bend thuscausing movement of the ultrasonic beam. Furthermore, it must obtainthis rigidity without adding significantly to the cross-sectional areaof the probe arm thereby increasing the drag as it moves through thefluid 30. The increase in drag would cause an increase in the load asseen by the oscillatory motor 90 thereby slowing down its scan rate. Inaccordance with the present invention, probe arm 100 is provided with astructure of sufficient rigidity so as not to bend or flex duringoscillation of shaft 112 of motor 90 while having minimal drag as arm100 moves through fluid 30. In particular, probe arm 100 extends in adirection substantially perpendicular to the longitudinal axis of themotor shaft 112, i.e. extends in a substantially horizontal direction asviewed in FIG. 1, and probe arm 100 comprises a pair of arm sectionsspaced apart in a direction substantially parallel to the longitudinalaxis of motor shaft 112, i.e. vertically spaced apart as viewed in FIG.1, so that probe arm 100 has sufficient rigidity so as not to bend orfled during oscillation of motor shaft 112. In addition, the armsections have surfaces disposed in planes substantially parallel to thelongitudinal axis of motor shaft 112, i.e. in substantially verticalplanes as viewed in FIG. 1, which surfaces have a sufficiently smallarea so as to minimize drag as probe arm 100 moves through the fluid.Thus, those surfaces of the arm sections define a biplanar probe armstructure.

Referring to FIGS. 1, 6 and 7, probe arm 100 includes a body portion 130at one end provided with a through bore or aperture 132 for mounting arm100 onto the output shaft 112 of motor 90. Probe arm 100 furtherincludes a first arm section 134 extending outwardly from the upper endof body 130 as viewed in FIGS. 1 and 6 in a direction generallyperpendicular to the longitudinal axis of bore 132 and a second armsection 136 extending outwardly from the lower end of body 130 at anangle to the axis of bore 132 which defines an acute angle with respectto arm section 134. As a result, the converging arm sections 134, 136define an open region or space 140 therebetween and meet to define asolid body portion 142 at the opposite end of probe arm 100. A throughbore or aperture 144 is provided in body portion 142 to receivetransducer 16 which is fixed therein. A first slot 146 extends inwardlyfrom bore 144 and joins a second slot 148 formed in the top surface 150of arm 100 as viewed in FIG. 7 to provide a path for an electricalconductor 154 shown in FIG. 2 extending from transducer 16 along the topsurface 150 of arm 100 and through an opening 156 in arm section 134 toexternal circuitry.

The two probe arm sections 134 and 136 provide a means of strengtheningprobe arm 100 while adding minimal drag while moving through fluid 30.As compared to a probe arm having a single section of a thickness equalto the sum of the thickness of arm sections 134, 136, the biplanar probearm 100 of the present invention provides a significant increase inoverall rigidity while keeping the total drag and inertia the same.

In the probe 10 shown in FIGS. 1 and 2, the motor of the transducer 16is oscillatory with an angle of oscillation of approximately ±20°.Although conventional brushless DC motors can be controlled to providethis motion, they are more complex than is really needed and as such aremore expensive. This complexity also carries over to the controlelectronics. Therefore, an oscillatory motor (a motor with limitedangular rotation) was selected for the motor 98 to move the transducer16 back and forth. These devices, often referred to as rotary solenoidsor brushless torque actuators, are very simple, low cost, and cangenerate very high torques which in turn can move the transducer 16faster. Furthermore, the control electronics is simplified by notrequiring the sophisticated hall effect sensor interface logic that isneeded for conventional brushless DC motors. By way of example, in anillustrative probe 10, motor 90 is a brushless torque actuatorcommercially available from Lucas Control System Products of Vandalia,Ohio.

Once the first motor means or oscillatory motor 90 has swept transducer16 across a singular line representing a path of the ultrasonic beamalong surface 14, the second motor means 92 is operated to step theassembly of transducer 16, arm 100 and motor 90 along a linear pathwhich is the second axis of scanning. Motor means 92 is a linearactuator comprising a small DC stepper motor with an integral lead screw170 attached so as to convert rotational motion into linear motion. Oncethe system control has sensed that the transducer 16 has completed aline scan, the linear actuator 92 is commanded to move along the secondaxis of motion by a single line. The motion of transducer 16 is thenreversed to sweep the ultrasonic scan back across the surface 14 in theopposite direction. This process is repeated until the desired area hasbeen scanned. The linear actuator 92 is then rewound to its startingposition in preparation for a new scan. A sensor, which will bedescribed, provides positional feedback to indicate that the linearactuator 92 has rewound to the starting position and provides a signalto the system control to halt the rewind process. By way of example, inan illustrative probe, linear actuator 92 is commercially available fromHayden Switch Instruments under model number 35862.

In the probe 10 shown in FIGS. 1 and 2 during preferred a mode ofscanning as described hereinabove, linear actuator 92 advances screw 170to move the assembly of transducer 16, arm 100 and motor 90 to the leftas viewed in FIGS. 1 and 2. When the scanning of a finger or othertissue is completed the assembly will be at its extreme left-wardposition where linear actuator 92 rotates screw 170 in the reverse orrewind direction. In order to determine when the full return position ofthe assembly is reached, there is provided position sensing meansgenerally designated 180 responsive to proximity of a detectablecomponent of the assembly for signalling when transducer 16 has moved apredetermined distance along the linear path, i.e. when the full returnposition of the assembly is reached. Sensing means 180 comprises aphotoelectric or optical sensor having a housing 182 fixed to end wall44 by a bracket 184 and having a recess or open region 186 facing towardthe linearly movable assembly and having the optical beam or paththerein. Sensor 180 is located so that when the full return position isreached, the periphery of the code wheel of encoder 110 enters recess186 and breaks the optical path thereby causing an indicating signal.Thus, sensor 180 operates in the manner of a limit switch.

A number of the electrically-operated components of probe 12, includingtransducer 16, motors 90 and 92, encoder 110 and sensor 118, and limitswitch 180 operate fully submersed in the oil 30. As such, theelectrical connections for these components are also submersed in theoil. Each electrical connection must therefore be brought out of the oilto its corresponding interface circuitry. To do this, two hermetic sealsare used. These seals, designated 190 and 192 in FIG. 1, contain thenecessary number of wires to bring a all of the power, grounds andsignal wires to and from the various electrical components housed withinthe oil. The only signals no brought out in this fashion are the power,ground and signal associated with the ultrasonic transducer 16. Thesesignals are carried on conductor 154 which is a miniature coaxial cableand sea Led separately from the rest of the wires. By way of example, inan illustrative probe, hermetic seals 190 and 192 are of the threadedplug variety commercially available from PAVE Technology Co., Inc. underthe designation PAVE-Seal.

As previously described, the addition of a third channel on the opticalencode wheel of encoder 3.10 provides an absolute position indicationwhich is needed for repeatable, high quality images. However, if thediameter of the code wheel is sufficient to increase the load inertiaand thereby reduce the scan speed of the oscillatory motor 90, analternate approach can be employed. This approach uses a conventional2-channel optical encode wheel and achieves the third channel positionindication by an external sensor. This sensor is an infrared LED andphotosensor reflectometer designated 200 in FIG. 8. It is positioneddirectly under the probe arm 100 approximately 10° from center position.When the probe arm is not over the sensor 200, no reflection of theinfrared beam 202 occurs and the photosensor indicates such. When theleading edge of the probe arm 100 covers the sensor, optical reflectionoccurs and drives a signal for the control electronics. This signal isused to latch in the state of the optical encoder bits to De read andcompared to a previously stored count for comparison. As a result, theoverall effect is the same as that provided by an integrated thirdchannel on the optical encode wheel without the increase in loadinertia. Thus, sensor 200 comprises means spaced from arm 100 anddetectably coupled to arm 100 for indicating a reference position of thearm.

The supporting means or platen 12 creates the interface between thefinger and fluid path of the ultrasonic transducer 16. If must be ofsufficient mechanical strength to provide a rigid support for the fingerduring the scan process. Deflection or deformation of the platen 12could result in a distorted image and make the post processing softwaremore difficult. Ideally, the acoustic impedance of the platen 12 mustmatch the skin of the finger as close as possible. Furthermore, since itis highly desirable to place a finger onto the platen 12 without the useof any types of acoustic coupling, the platen interface must be able tofully contact the surface of the finger, minimizing any air gapsin-between. All of these requirements coupled with the ability of theplaten 12 to pass high frequency ultrasound without appreciableattenuation or frequency down shift must be met in order to obtain highquality images of the finger.

Platen 12 is constructed using a cross-linked polystyrene or perspexmaterial coated with a thin layer of silicone RTV. The body ofpolystyrene or perspex material has an acoustic impedance very near thatof human tissue and a thickness suitable to provide the necessarymechanical rigidity and provide as short an ultrasonic path as possible,for example a thickness in the range of {fraction (1/16)} inch to ⅛inch. Ultrasonic frequencies of 30 MHz are able to propagate through thematerial without appreciable modification. In order to provide maximumcoupling to the finger, if desired the platen 12 can be coated on theexternal surface contacted by the tissue being image with the thin layerof silicone RTV. Other types of silicone latex rubber can be employed.The RTV improves the mechanical coupling to the finger while maintainingthe proper acoustic impedance. The RTV must be of sufficient thicknessso as to be able to range gate out the polystyrene/RTV return echoes andprocess only those echoes associated with the RTV/finger interface. Therequired thickness of RTV is dependent upon the overall “Q” of thetransducer 16. By way of example, in an illustrative system, the platenbody has a thickness of about {fraction (1/16)} inch to ⅛ inch and thecoating has a nominal thickness of about 0.010-0.030 inch.

Platen 12 is sealed in cover 36 thereby maintaining the fluid-tightintegrity of the probe structure. The outer surface of platen 12 can besubject to wear over a period of time thereby requiring fieldreplaceability of platen 12. These two requirements can be satisfied bya two piece platen 12′ as shown in FIG. 9 comprising a first or innerlayer 220 which is permanently sealed to cover 36 and maintains thefluid-tight integrity of the probe structure. A second or outer platenlayer 222 is coupled to the first layer by an acoustic gel 224 or thelike and is easily removable for replacement. The outer surface of layer222, which is contacted by the tissued being imaged, can be providedwith a coating 226 like the silicone RTV coating previously described.

Two forms of transducer 16 can be employed depending upon the type ofscanning. A high frequency transducer of approximately 30 MHz, with anaperture of approximately 0.180″ and a focal length of approximately0.25″ can be used for fingerprint imaging. This transducer provided thehighest resolution, i.e, smallest spot size, but was not significantlyattenuated due to the limited depth of penetration into the finger. Asecond transducer of similar physical characteristics but reduced infrequency to approximately 15 MHz can be used for the subdermal scanningthat was targeted at artifacts other than the fingerprint structure. Forthis imaging, the 30 MHz ultrasound would be so significantly attenuatedthat the cost of the signal processing electronics would be prohibitive.Therefore, by dropping in frequency by a factor of 2, a much strongersignal is received.

A principal requirement on transducer 16 is to minimize the overall spotsize which it generates. The spot size is a function of the frequency ofthe transducer, aperture and overall focal length and is given by:

d=2.44(f _(L) /D)λ

where d is the spot size measured at the zero crossing points, f_(L) isthe transducer focal length, D is the transducer aperture and λ is thewavelength of the soundwave. In the design of a transducer, it isdesired to keep the ratio f_(L)/D as small as possible. This can beaccomplished using a variety of well-known techniques such as anexternal focusing lens, a curved transducer element or a combination ofboth. By way of example, in an illustrative system, transducer 34produces a spot size of 0.002 inch measured at −6 db points perASTME1065 and has a ring time of 1 cycle measured at −20 db down frompeak. Cable 154 is Cooner coaxial or the equivalent having a diameter ofabout 0.037 inch. An illustrative commercial form of transducer 34 isavailable from Krautkramer Bransen under model no. 389-005-860.

As previously described, a typical scan area of surface 14 hasdimensions of 0.75 inch by 0.75 inch. There are some applications, suchas NCIC 2000 law enforcement initiated by the F.B.I. that call forlarger scan areas up to a maximum of 0.88″×1.22″. The scan geometry ofthe probe 12 of the present invention meets the increased arearequirements. In order to do this, several components need to bechanged. To increase the scan length (y-axis) from 0.75″ to 1.22″, thelinear actuator 92 must be stepped an additional 235 steps(0.002″/step). The linear actuator 92 has sufficient travel and thusrequires only a software change to the control electronics. To increasethe scan width from 0.75″ to 0.88″ (the x-axis), several components needto be changed. It was determined that rather than drive the oscillatorymotor 90 at a larger angle, the length of the probe arm 100 should beincreased. Thus for the same angle of sweep, larger segments can bescanned. In fact, an optimum probe arm length of 1.3″ is used. This inturn requires a scan angle of ±21.3°. The reduced scan angle has theadded benefit of increasing the scan frequency thereby reducing theoverall scan time. As a result of the reduced scan angle, faster moreefficient forms of oscillatory motor could be used for the oscillatorymotion. The increase in probe arm length to 1.3″ requires a change inthe resolution of the optical encoder 110 in order to sample at therequired spatial frequency. The optical encoder 110 was increased from512 lines per revolution to 1024 lines per revolution. This resolutionin code wheel 119 coupled with the circuitry of decoder 118 results in aangular resolution of 0.087°. This maps to a linear scan resolution ofone sample per 0.002″.

Due to the arc-scanning motion of the ultrasonic transducer 16, data iscollected in a non-linear fashion along this axis, i.e. the x-axis.Specifically, the data is not collected line by line but rather arc byarc. In addition, the amount of distance swept out between pixels nearthe center of the scan varies from the edges of the scan. As a result,this skew or distortion must be corrected. This correction is a mappingof pixels in one geometric space to pixels in another geometric space.Naturally, this mapping is not a one to one mapping. The pixel to beplaced in the corrected geometric space is often from a point betweenpixels of the original geometric space. As such, the data values or greyscale values must be determined. Therefore, in effect, two axes oflinearization are taking place, hence the name bilinearization. Thefirst correction is the placement of pixels from the input geometricspace to the output geometric space. The second correction is thedetermination of what grey scale value is to be used.

With respect to the mapping of the input geometric space to the outputgeometric space, this is nothing more than a simple table lookup method.The values in the table are determined according to the followingmethod. The first step is to find the actual coordinates of each scannedpixel along the scan arc. Assume, for example, pixel number 256 islocated at a scan angle of 0° along the arc.

O₂₅₆=0°

X₂₅₆=0.750 (inch) sin 0°

Y₂₅₆=0.750 (inch) cos 0°

where 0.750 inch is the length of the scan arc previously described,Pixels on either side are offset with respect to pixel 256. Thus,

O₂₅₅=(255-256) (90°/512)

X₂₅₅=0.750 (inch) sin (−0.1758°)

Y₂₅₅=0.750 (inch) cos (−0.1758°)

O₂₅₇=(257-256) (90°/512)

X₂₅₇=0.750 (inch) sin (−0.1758°)

Y₂₅₇=0.750 (inch) cos (−0.1758°)

where 512 is the encoder resolution of 512 lines per revolution.

The next step is to change the foregoing actual coordinates into pixelcoordinates-by dividing by 0.002 inch since a scan sample is taken every0.002 inch.

X₂₅₅=X₂₅₅/0.002 =−1.15

Y₂₅₅=Y₂₅₅/0.002 =375

X₂₅₆=X₂₅₆/0.002 =0

Y₂₅₆=Y₂₆₅/0.002 =375

Then the middle pixel #256 is centered at location 256 by shifting all Xcoordinates by +256.

X₂₅₅=−1.15 +256 =254.85

X₂₅₆=0 +256 =256.00

The next step is to shift the Y coordinates by −265.15 (make Y=0 at ascan angle of 45°);

0.750 (inch) cos 45°/0.002 inch −265.15

Y₂₅₅=375−265.15 =109.85

Y₂₅₆=375−265.15 =109.85

Finally, for each new line scanned, Y positions are offset +1 from thelast line due to the linear movement of 0.002 inch per line.

line 1 : Y₂₅₀=109.85

line 2 : Y₂₅₀=110.85

line 3 : Y₂₅₀=111.85 etc.

Thus, the table look up values for the mapping of the input geometricspace to the output geometric space are obtained according to theforegoing method.

Regarding the selection of the proper grey scale value, this can beaccomplished by taking a weighted average from the surrounding four datapoints. This process is given by the following equation:

(i,j)=(1−i′){j′(i,j+1)+(1−j′)(i,j)}+{j′(i+1,j+1)+(1−j′)(i+1,;)}

where

i,j =input image data point

i′,j′=output image data point

In order to make this mapping in real time, a high speed DSP chip isused. This processor collects the data line by line and maps it to theproper output while correcting its greyscale amplitude. This is done inreal time and is overlapped with the scan time of the scanner itself,thereby causing minimal throughput delays. A block diagram of theBi-Linearization processor is given in FIG. 10.

The processor is centered around a DSP chip 240 which, by way ofexample, can be a Motorola 56166 processor. Incoming data from thescanner on line 242 is interfaced by a data buffer 244 and is sent toprocessor 240 via the bi-directional data busses 246 and 248. Apermanent memory or flash PROM 250 stores the program used by theprocessor 240. A dynamic RAM or external memory 252 stores data for useby processor 240. The bi-directional data bus 248 is connected to bothmemories 250 and 252. A controller 256 is provided for DRAM 252, and adecoder 258 is associated with the control of processor 240. Processeddata from chip 240 is transmitted over the bi-directional data busses248 and 246 to a buffer/latch 262 which interfaces with a parallel part264 of the system computer. Processor 240 is connected via a leveltranslator 268 to a serial part 270 of the system computer. A watchdogtimer 274 and a debugging part 276 also are associated with processor240 in the manner shown.

Turning now to the various modes of scanning, acquiring images from thesurface of the finger or near the surface of the finger such as in thecase of subdermal fingerprint imaging, the amount of attenuation of theultrasonic signal is minimum. Therefore, in order to obtain maximumspatial resolution, the frequency of the transducer 16 is very high. Forthis application, the frequency of the transducer is approximately 30Mhz. In order to capture images from structures just below the surfaceof the finger, ah electronic range gate is used to allow only thoseechoes returned from the depth of interest to be processed. Therefore,the only modification to the system to process surface fingerprintimages versus subdermal fingerprint images is in the application of therange gate. The timing of this range gate can be controlled by softwaremaking it a transparent change to the person that is being imaged.

In both cased the ultrasonic energy enters the finger at a 90 degreeangle to the surface of the finger. Orienting the transducer 16 in thisfashion gives the maximum signal strength possible. However, thespecular reflections from the front and back sides, respectively, of theplaten 12 are also returned to the transducer 16. This is not a problemfor surface imaging since they can be range gated out. However, for deepsubdermal imaging, the multipath specular reflections can represent asevere problem when trying to image at particular depths. Therefore, thetransducer 16 must be oriented in such a way as to eliminate theseechoes.

When images from deeper in the finger are of interest, the amount ofattenuation of high frequency ultrasonic signals is so significant thateither the signal is lost altogether or the gain bandwidth product ofthe amplification stages found in the system signal processor become solarge that the cost of the system is prohibitive. Therefore for imagingthese structures, a lower frequency transducer 16 is used, for exampleat 15 Mhz. This solves the/problem of high attenuation at the cost ofslightly reduced spatial resolution. However, the loss of resolution isnot critical since the subdermal structures of interest are larger thanthe ridge structures found on the surface of the finger.

A secondary problem that can occur when imaging deep inside the fingeris that depending on the depth at which the echo is to be collected, amultipath echo from specular reflectors that fall in the path of thesound wave may shadow the artifact of interest. Therefore, the multipathechoes that are caused by the specular reflectors need to be removed soas to enable imaging of the actual signals of interest. This can beaccomplished by rotating the transducer 16 off axis by a small number ofdegrees sufficient to cause the specular return echoes to be missed.This causes any echoes due to a smooth surface to reflect at an anglesuch that the return echo never makes it back to the transducer 16. Onlythose echoes that scatter the sound wave in all directions can be seenby the transducer 16. Most structures of interest internal to the bodywill tend to scatter the soundwave, thereby making this technique veryeffective for this scanning application.

The industry standard for fabricating lenses for focusing ultrasound isto use a fixed radius to create the curvature of the lens. The lensmaterial is normally made from polystyrene and is machined down to thedesired size and curvature. This geometry is responsible for definingthe focal length of the transducer and the spot size. However, analysisof the lens equation readily shows that constant radius lenses do notprovide a diffraction limited spot size. They cause sphericalaberrations which have the effect of blurring or enlarging the size ofthe focused beam. Therefore, in order to reduce the size of the spot tothe theoretical minimum, a non-spherical shaped lens, a curvedtransducer element or a combination of a curved element andnon-spherical lens must be employed.

FIG. 11 is a block diagram of an ultrasonic imaging system of whichprobe 10 is a part. The motion of the probe or mechanical scanner 10 iscontrolled by torque controller 300 which includes a micro-controller302, optical encoder interface 304 and angle correction switches 306which will be described. A signal processor 310 energizes transducer 16and data from transducer 16 is received by signal processor 16 whereamplification, range gating, peak detection and A/D conversion takeplace. Voltages for operating the system are obtained from a powersupply 312 and regulator 314. The bilinearization processor of FIG. 10is connected to signal processor 310 via bus 318. It stores data andalso corrects for any geometric distortion caused by the arc scanningmotion.

Torque controller 300 functions to ensure that the scan of oscillatorymotor 90 is consistent in its absolute position from scan to scan. Thescanner 10 at the time of assembly is calibrated. This calibration is tomove the probe arm 100 from its center position until the third channel(IDENT) marker fires. The IDENT marker can be implemented either as thethird channel of the optical encoder 110 or by the external arc limitswitch 200. Once this fires, the output of the optical encoder 110 isread. This output represents the total angle or distance the absoluteIDENT marker is from zero position. This value is now entered onto anangle correction or DIP switch 306 located on the torque controller 300.

During normal operation, the motor 90 comes to rest at a slightlydifferent spot at the end of every scan. It does not consistently returnto the zero position. As a result, the final resting spot of the motor90 would become the zero position for the next scan. As such, theposition of each scan would vary from scan to scan. In the improvedimplementation provided by torque controller 300, at the beginning ofeach scan the motor 90 is oscillated momentarily without the fingerbeing imaged. During this time, the output of the optical encoder 110 isread by the torque controller 300 at the firing of the IDENT signal. Thevalue seen here should match the value stored on the DIP switches 300which were previously set at the time of calibration. Thus, the torquecontroller 300 reads the DIP switches 306 and does a comparison. If thevalues do not match, the torque controller software adjusts the scanangle an amount equal to the difference between the switch setting andthe actual read value. Doing such, ensures that the scan will beperfectly centered every time resulting in very consistent images.

FIGS. 12-16 illustrate alternate architectures which address the issueof providing the highest possible scan speed while providing thesmoothest and quietest operation of the scanning device. In the probe 10of FIGS. 1-8, the transducer 16 is moved in an oscillatory fashion by abrushless torque actuator 90. The mass of the transducer 16, itsdistance from the point of rotation and its hydrodynamic drag in the oil30 all add to the inertial load of the system. This load is sufficientenough to put tremendous torque requirements on the actuator 90. Thetorque requirements are high enough to impose limits on the speed atwhich brushless torque actuators can drive the probe arm assembly.Therefore, in accordance with the present invention, in order to assistthe oscillatory motion of the motor 90, an external spring can be added.One type of spring, known as the flexural bearing, is particularlysuited for this application. It is a spring which is designed to flex inboth directions and when properly designed, will have infinite life.

FIG. 12 shows one form of spring means operatively associated with motor90′ to assist the oscillatory motion of the motor. The spring means orflexual bearing means is mounted external to motor 90′ and is thesimplest of configurations requiring no rework to the motor 90′. Asshown in FIG. 12, the flexual bearing means comprises flat, crossedsprings 330, 332 supporting rotating sleeves 334, 336. One of theflexual bearing sleeves 334 is attached by a member 340 to the motoroutput shaft 112′. The other of the flexual bearing sleeves 336 isattached to a shell 342 fixed to the housing of motor 90′. An outputcoupling in the form of a disc 344 is connected by a member 346 to themovable bearing sleeve 334. Disc 344, in turn, would be fixed to the endof the probe arm which carries the transducer at the other end. Thearrangement of FIG. 12 provides scan frequencies significantly greaterthan those obtained with the motor alone.

FIG. 13 shows another form of spring means operatively associated withmotor 90′ to assist the oscillatory motion of the motor. The springmeans or flexual bearing means replaces the rotor assembly with themagnets mounted directly on the flexual bearing. The arrangement can behoused in the same actuator enclosure without adding any additionalheight to the overall assembly. As in the embodiment of FIG. 12, theflexual bearing means comprises flat, crossed springs 330′, 332′supporting rotating sleeves 334′, 336′. In this embodiment, however, oneof the flexual bearing sleeves 334′ has the motor rotor magnets 350mounted thereto on the outer surface of sleeve 334′ and facing the motorstatic coils 352. The other of the flexual bearing sleeves 336′ isattached to the motor shell or housing 354. An output coupling in theform of disc 344′ is connected by a member 346′ to the movable bearingsleeve 334. Disc 344′, in turn, would be fixed to the end of the probearm which carries the transducer at the other end. The arrangement ofFIG. 13 provides scan frequencies significantly greater than thoseobtained with the motor alone.

By way of example, in the illustrative embodiments of FIGS. 12 and 13the flexual bearings comprising flat, crossed springs supportingrotating sleeves are commercially available from Lucas Aerospace PowerTransmission Corp. under the designation Free-Flex Pivot frictionlessbearing.

In the probe of FIGS. 1-8 in which both motor 90 and linear actuatoroperate in an oscillatory mode large amounts of energy are expended.Much of this energy is used in simply starting and stopping the motors90, 92 themselves and only a fractional part of the energy is used inactually driving the transducer. In order to minimize much of the torquerequirements of the motors and thereby minimize the energy consumed, itis proposed that a continuously rotating motor be used.

There are several advantages to the continuously rotating motorapproach. Eliminating the need for high torque, oscillatory motionmotors and replacing them with very low torque continuously rotatingmotors reduces the overall cost of the system. The RPM of the motor canbe driven at very high speeds which will result in scan frequencies muchhigher than that attainable by the oscillatory approach. The largeenergy draw in starting and stopping the rotor of the actuator isvirtually eliminated thus reducing the overall power consumption of thedevice. Oscillatory motion on ball bearings causes very high rates ofwear. This will eventually result in bearing play which will cause theimage quality to degrade. Using a continuously rotating approach willprevent the bearings from wearing out excessively early therebyimproving overall reliability of the system.

One type of architecture for implementing a continuously rotatingscanner, i.e., a continuously rotating transducer is shown in FIG. 14. Atransducer 360 is mounted directly onto a flywheel 362 similar to arm100 of FIG. 1 and is continuously rotated. The flywheel 362 is connectedat the other end to the output shaft 364 of a motor 366. When thetransducer 360 passes under the area of interest, data is collected.This approach is able to use a very low power low cost motor 366 fordriving the flywheel transducer assembly. The only issue becomes one ofhow to couple the cable 370 of the ultrasonic transducer 360, which iscontinuously rotating, to the signal processor circuit card. There areseveral solutions for this problem, one of which is the use ofcommercially available slip rings. The stationary portion 372 of theslip ring can be mounted to the base 374 of the scanner where stationarywires 376 are attached and connected to the signal processor circuitcard. The contact portion 380 of the slip rings can then be attached tothe motor shaft 364 and wires 370 attached to it which lead to thetransducer 360. In this manner, contact via the slip rings can bemaintained to the signal processor while the motor 366 is rotating.

A variation on this approach could be made by adding multipletransducers around the perimeter of the flywheel. The multipletransducers will reduce the amount of idle time while the transducerrotates around into position. Thus, adding a second transducer willreduce the scan time by 50%. A third transducer will reduce the originalscan time by 66%, and so on. Implementing the multiple transducerapproach will require some simple modifications to the systemelectronics. One modification could be to add a Signal Processor circuitboard for every transducer that is added. This of course is an expensiveapproach but extremely easy to implement. Another approach would be tomultiplex the front end portion of the pulser/receiver electronics andselectively pulse and receive echoes from each transducer. This would bethe most cost effective solution. The foregoing is illustrated in FIG.14a.

FIGS. 15 and 16 illustrate an alternative form of probe wherein scanningis performed linearly in both the X and Y directions. A continuouslyrotating motor 390 has an output shaft 392 connected to a flywheel 394which in turn drives a pivoting arm 396. The pivoting arm 396 carries atransducer 398 33 at the other end which rides back and forth on alinear bearing support 400. As the motor 390 rotates, the pivot arm 396drives the transducer 398 linearly back and forth along the path of thelinear bearing 400. This is accomplished without reversing the motion ofthe motor 390 itself. Once the motor 390 is driven up to speed, theflywheel 394 overcomes the inertia of the motion of the transducer 398.The cable (not shown) connecting the transducer 398 to the signalprocessor simply has to flex in and out by the same amount as the linearmotion of the movement of the transducer. Position feedback of thetransducer can be accomplished by either attaching an optical encoderonto the motor shaft as previously done or by using a linear feedbackdevice attached to the linear slide bearing 400. This device could be asensor such as linear optical encoders, LVDT'S, linear potentiometers,etc. The second axis of motion would then be accomplished in the samefashion as done in the probe of FIG. 1, i.e., by a linear actuator 410comprising motor 412 and screw 414 which moves the entire structure 416supported in the linear bearings 418, 420. Thus the arrangement of FIGS.15 and 16 provides linear scanning movement of transducer 398 inmutually orthogonal directions, i.e., X and Y directions.

There can be-applications requiring the probe 10 of FIGS. 1-11 tooperate at low ambient temperature conditions. At least one temperaturesensor such as a thermistor 430 can be located within cavity 28 forexposure to fluid 30 to monitor the temperature of the same. If desiredanother temperature sensor can be provided to monitor the ambienttemperature. When thermistor 430 indicates that the temperature of fluid30 is below a desired level, a control 436 signals microcontroller 302to pulse energy through motor 90 rather than oscillating the motor. Thispulsing of motor 90, i.e. simply applying the same polarity signals tothe motor rather than reversing the polarity, has the effect of warmingthe fluid 30. This would be continued until thermistor 430 indicatesthat the temperature of fluid 30 has risen to the desired level.

FIG. 17 illustrates the scanner of the present invention configured inan identification system which takes the image obtained from the scannedfinger and compares it to a large database of previously scanned imagesto determine if a match exists. These identification systems, whichtypically are quite large and used by law enforcement agencies,immigration services and the like, have been generically termed AFIS orAutomatic Fingerprint Identification Systems. Referring to FIG. 17 theultrasonic biometric reader 450 comprises the scanner according to thepresent invention including probe assembly 10, signal processor 310,torque controller 300 and power supply/regulator 312, 314. There isprovided means in the form of mass storage device 452 for storing adatabase of previously stored images, i.e. stored fingerprint images.There is also provided a system processor means 454 having inputscoupled to database storage means 452 and to the output of the processorin ultrasonic biometric reader 450 for comparing a scanned image fromreader 450 to the previously stored images in device 452 to determine ifa match exists. FIG. 17 also illustrates a second-combination ofultrasonic biometric reader 450′, mass store device 452′ and processor454′ with local, area network means 456 for connecting the processors454 and 454′ together.

FIG. 18 illustrates an alternative arrangement wherein the hard-wiredcommunication link between ultrasonic biometric reader 450 and processor454 is replaced by a wireless communication link such as an RFtransmitter/receiver 460 connected to the output of biometric reader450, an RF transmitter/receiver/462 connected to the input of processor454 and the transmission medium 454 therebetween. As a result, theultrasonic biometric reader 450 can be located in a remote or mobilearea such as a police car or other remote data entry site. A finger isplaced on the reader, scanned and the data transmitted in a wirelessmanner to an AFIS processor for processing. The communication link isbi-directional and transmits back to the reader any pertinentinformation. Other wireless communication links can be employed such asoptical, ultrasonic and the like.

FIGS. 19 and 20 illustrate the scanner of the present inventionconfigured in a verification system where a finger is scanned andcompared to a single reference print to verify if the individual is whohe claims to be. This type of system is much less complex in nature ascompared to identification systems since it does not require theextensive searching that larger AFIS system must do, which require highspeed processors, large databases, etc. One method of implementing sucha system is using smartcards or any other type of portable data storagedevice such as a mag-stripe card, optical storage card, semiconductorstorage card and the like. Smartcards are plastic cards similar in sizeto a standard credit card for carrying by persons. The traditionalmag-stripe found on the back of the card is either replaced orsupplemented by an on board microprocessor. The microprocessor has builtin memory which enables two options for overall system configuration. Afirst option is to simply encode the biometric data into the memory ofthe smartcard. A person wishing to have his identity verified places hisfinger on the ultrasonic reader and the finger is scanned. The data isthen read out of the smartcard presented by the individual and acomputer is used to compare the two images. This is illustrated in FIG.19 wherein an ultrasonic biometric reader 470 comprises the systemaccording to the present invention including probe assembly 10, signalprocessor 310, torque controller 300 and power supply regulator 312,314. A record member 472 in the form of the smartcard mentioned abovehas storage means containing a recorded biometric image, i.e. forstoring a recorded fingerprint image. A processor means 474 has a firstinput for receiving output signals from the ultrasonic biometric readerand a second input for receiving a signal representation of the recordedimage to determine if a match exists between the scanned and recordedimages. Thus, in the arrangement of FIG. 19 the record member 472 andprocessor 474 are physically separate.

A second option is similar to the first option with the main differencebeing that the computer used to compare the two images is replaced bythe processor of the smartcard. Thus, the smartcard not only containsthe biometric data of the finger but is also responsible for comparingthat data to the scanned data of the finger. This is illustrated in FIG.20 wherein a smartcard or record member 480 has storage means containinga recorded biometric image and processor means 482 thereon having oneinput for receiving output signals from the ultrasonic biometric reader470′ and a second input for receiving a signal representation of therecorded image to determine if a match exists between the scanned andrecorded images. Thus, in the arrangement of FIG. 18 the record member480 and the processor 482 are physically integrated.

FIG. 21 illustrates an alternative arrangement wherein the hard-wiredcommunication link between processor 474 and ultrasonic biometric reader470 and record member 472 in the arrangement of FIG. 19 is replaced by awireless communication link. The wireless communication link comprisesan RF transmitter/receiver 490 connected to the outputs of biometricreader 470 and record member 472, an RF transmitter/receiver 402connected to processor 474 and the transmission medium therebetween. TheRF communication link is bidirectional, allowing match results to besent back to the reader subsystem. Other wireless communication linkscan be employed such as optical, ultrasonic and the like.

It is therefore apparent that the present invention accomplishes itsintended object. While embodiments of the present invention have beendescribed in detail, that is for the purpose of illustrations, notlimitation.

What is claimed is:
 1. A probe for an ultrasonic imaging system forproviding an output ultrasonic beam to scan human or animal tissuehaving a surface, said probe comprising: a) means for defining saidsurface in a manner rigidly supporting said human or animal tissue forimaging the same; b) transducer for providing an output ultrasonic beam;c) electrically-operated motive means operatively coupled to saidtransducer for moving said transducer in a manner such that said outputultrasonic beam is directed in a path along said surface; d) afluid-tight housing extending from said surface defining means andhaving an interior region containing said transducer and said motivemeans; e) a fluid filling said interior region of said housing, saidfluid having an acoustic impedance substantially equal to that of waterand having a viscosity sufficiently low so as not to impede the movementof said transducer and being electrically non-conductive; f) an armstructure for directly said motive means to said transducer; and g) anencorder operatively associated with said motive means for providingpositional information relating to said motive means.
 2. A probeaccording to claim 1, wherein said fluid comprises mineral oil.
 3. Aprobe according to claim 1, wherein said motive means comprises: a) amotor having an output shaft for providing oscillatory output motion; b)means for coupling said output shaft to said transducer so that inresponse to oscillation of said shaft said output ultrasonic beam isdirected in an arcuate path along said surface; and c) mean for movingsaid transducer in a manner such that said output ultrasonic beam isdirected in a linear path along said surface and in a radial directionrelative to said arcuate path.
 4. A probe according to claim 1, whereinsaid means for defining said surface comprises a platen of a materialhaving an acoustic impedance substantially matching the acousticimpedance of the tissue being imaged.
 5. A probe according to claim 4,wherein said platen comprises a first section permanently sealed to saidhousing means and a second section defining said surface and removablefrom said first section for replacement.
 6. A probe according to claim1, wherein said means for defining said surface comprises a platen inthe form of a body of material having an acoustic impedancesubstantially matching the acoustic impedance of the tissue being imagedand having sufficient mechanical strength to support the tissue withoutdeflection or deformation.
 7. A probe according to claim 6, furtherincluding a coating on said body of a material which improves mechanicalcoupling of said body to the tissue being imaged while maintaining thematching of acoustic impedance.
 8. A probe according to claim 1, whereinsaid transducer is operatively coupled to said motive means by means forpositioning said transducer closely adjacent said supporting means in amanner directing said ultrasonic beam on said surface and so that thesize of said beam at its focal point is as small as possible to maximizethe resolution of said system.
 9. A probe according to claim 1, furtherincluding hermetic seal means in said housing and electrical conductormeans extending from said motive means through said seal means.
 10. Aprobe according to claim 1, further including means operativelyassociated with said housing for accommodating thermal expansion andcontraction of said fluid.
 11. A probe according to claim 1, furtherincluding sensing means in said interior region of said housing formonitoring the temperature of said fluid.
 12. A probe according to claim11, further including means operatively connected to said sensing meansfor heating said fluid when said sensing means indicates that thetemperature of said fluid is below a predetermined level.
 13. A probeaccording to claim 11, further including control means operativelyconnected to said sensing means and to said electrically operated motivemeans for supplying electrical power to said motive means in a mannercausing said motive means to release heat to said fluid when saidsensing means indicates that the temperature of said fluid is below apredetermined level.